This application claims priority of 199 25 343.9, filed on Jun. 2, 1999, the disclosure of which is expressly incorporated by reference here.
The present invention relates to a transfer system. The transfer system according to the invention is used particularly for workpiece transport in forming machines, such as transfer presses or other machines, where workpieces must be guided through several machining stations.
As a rule, forming machines, such as large-part transfer presses (vehicle body presses) have a succession of machining stations, such as press stages, through which the workpieces pass successively. They experience another deformation in each station along their path, so that the desired end product is created in steps. The overall machining time of a workpiece is composed of the times required for the workpiece forming as well as the transport times. The productivity of a press system or other machine can be increased if its output, that is, the number of parts produced per time unit, is raised. If the stroke rate is increased for this purpose in the case of a press, that is, the rotational speed of the main press drive is raised, the transport times cannot remain unchanged but decrease correspondingly.
Sheet metal parts to be moved in large-piece transfer presses are frequently relatively large. In the transport direction, they may be 1 m to 2 m long and, transversely to the transport direction, may be over 4 m wide. Together with corresponding workpiece holding devices, the total mass is therefore considerable, which must be accelerated and braked during the transport from one tool to the next. In this case, the paths to be covered are within the range of several meters; in the case of press systems with intermediate depositing devices, for example, at 2 m to 3 m. However, the workpiece transport can take place only in a very narrow time window; that is, the transfer movement must be coordinated relatively precisely to the work of the remaining press system.
When designing press systems, care must be taken that the press system can also be used for future vehicle body designs (or other shapes of parts). It should therefore be expected that tools are used in the press whose precise construction is still unknown at the point in time of the manufacturing of the press system. Correspondingly, it may be required to adapt the transfer movement when setting up the press or when retooling to the changing conditions.
DE 2741808 discloses a transfer device for transfer presses having two transport rails extending at a distance in parallel to one another along several stations. The transport rails can be lifted and lowered, for which lifting mechanisms are used which are driven by electric motors arranged at the end side. A longitudinal movement of the gripper rails is caused by electric motors arranged on a base frame and acting upon toothed racks connected with the gripper rails. A longitudinal movement of the toothed racks is therefore transmitted to the gripper rails. The transfer curve, which is achieved by superimposing a lifting movement with the transfer movement, is achieved by an electronic sequence switching which controls the motors starting from mechanical curves. Between the driving motors and the moved transfer rails, power transmitting devices, which have an inert mass, are required.
Furthermore, a three-axis transfer device is described in DE 4310057 A1 for the transport of workpieces in transfer presses. Two transfer rails, which are spaced at a distance parallel to one another, are used for the workpiece transport. The transfer rails are moved toward one another and away from one another for picking up and depositing the workpieces. They can be lifted and lowered and can be moved in the transport direction for causing the transport. Electric motors are used for driving all movements. The electric motors causing the transfer step are arranged on a fixed base frame which is arranged outside the machining (forming) stations. The base frame carries drive units which have a slide as an output which is displaceably disposed on a linear guide. This slide is connected with the respective assigned gripper rail by way of a connecting rod, so that the longitudinal movement of the gripper rail can be determined by the movement of the slide but it can be lifted and lowered independently thereof.
The inert masses to be taken into account for determining the overall dynamics also contain parts arranged outside the gripper rails, such as slides and connecting rods, which are used for the connection between the gripper rails and the drive units.
DE 19506520 A1 discloses a transfer device which is constructed as a two-axle transfer. Travelling carriages are longitudinally displaceably disposed on spaced parallel guide rails through a press system. A suction bridge is in each case arranged between two travelling carriages and has the purpose of temporarily receiving a workpiece and carrying it away. The suction bridges are assigned to two different groups. The suction bridges of the first group travel through a slightly different transfer curve than the suction bridges of the second group. They differ with respect to their longitudinal movement. Correspondingly, two stationarily disposed transfer drive units are provided. The first transfer drive unit has a vertically aligned linear guide which has a drive unit generating a linear movement for adjusting the position of the gripper devices, the drive unit being moved back and forth in the transfer direction. A slide provided on the linear guide is connected with a connecting rod driving the suction bridges which are assigned to the corresponding drive unit. A corresponding arrangement is provided for the drive of the suction bridges of the other group. In addition to moving the suction bridges and the connecting rods, the transfer drive units must also move the linear guides.